Network SouthEast (NSE) was one of the three passenger sectors of British Rail created in 1982. NSE principally operated commuter trains in the London area and inter-urban services in densely populated South East England, although the network reached as far west as Exeter. Before 1986, the sector was known as London & South Eastern.
In the privatisation of British Rail on 1 April 1994 it was gradually broken into a number of franchises.
Before the sectorisation of British Rail in 1982 the system was split into largely autonomous regional operations: those operating around London were the London Midland Region, Southern Region, Western Region and Eastern Region. Sectorisation of BR altered this setup by instead organising by the traffic type: commuter services in the south-east of England, long distance intercity services, local services in the UK regions, parcels and freight. The aim was to introduce greater budgetary efficiency and managerial accountability by building a more market-focused and responsive business, rather than privatising BR outright. It was expected that the London and South East sector would cover most of its operating costs from revenues, in contrast to heavily subsidised rural services.